1999 Civic Idle air control at 0 percent and setting a code

Jason Owner/Technician California Posted   Latest  
Unsolved
Driveability
1999 Honda Civic DX 1.6L (D16Y7) 5-spd (S40)
None

Idle seams normal and rests at about 700 RPM. The idle air control counts are at 0. Throttle is at 9 percent, there are not vacuum leaks, the throttle, idle air control valve, PCM and PCV valve have been replaced. Valves have been adjusted and timing belt has been replaced for maintenance and verification of repair. When I place my hand over the throttle to seal it, the engine stalls and holds vacuum for at least 30 seconds. I have reached my end. Thanks for all you help with this nightmare. I have called this one home for to long.

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Justin Technician
Georgia
Justin
 

Base ignition timing set correctly?

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Mark Technician
Wisconsin
Mark
 

Can you tell us what code is setting?

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Benjamin Owner/Technician
Georgia
Benjamin
 

Your service data should show a troubleshooting flow chart for p1509. Follow that flow chart. Ive seen G101 left loose accidentally when servicing the tstat.

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Helpful
David Mobile Technician
California
David
 

Making sure that ground at G101 is clean & tight is not enough. That ground path travels through the T/stat bolts that often corrode.

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Laird Owner/Technician
Nova Scotia
Laird
 

Has the throttle stop been adjusted to high?

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Elias Owner/Technician
California
Elias
 

Jason i dont see the code, but if its related to the tps or p050X they have lots of trouble with the throttle bodies. we generally do the throttle along with iac. set the tps and ship it

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Bentley Manager
California
Bentley
 

Does the idle adjusting screw (air bleed) make no difference in the iac count?

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Jason Owner/Technician
California
Jason
 

Thanks for all your help. I am very frustrated in this car. I have replaced the throttle with a used one, new one not available. The Idle screw is all the way in. It is a P0505 code that sets. I have adjusted the throttle stop as low as I can without sticking the throttle. I have exhausted all my patience with this car.

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Bentley Manager
California
Bentley
 

I assume plugging iac port makes no difference? According to diag chart incorrect ect can cause the code. What are the idle fuel trims?

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Elias Owner/Technician
California
Elias
 

And you replaced the iac valve with a genuine unit as well? Or used? Or aftermarket?

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Craig Diagnostician
Illinois
Craig
   

Jason, have you tried pinching off the PCV valve hose or the canister purge valve? I have seen PCV valves break and possibly an incorrect valve as I see it was swapped out create a vacuum leak inside the crankcase on older Honda's. The purge valve is also something to consider as well. Also check the EGR valve I have seen some flow ever so slightly at idle, dropping engine vacuum slightly which…

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Kerry Mobile Technician
Ohio
Kerry
 

Would the fact that he plugs off the throttle body and it both dies and holds vacuum for 30 seconds rule out possibilities like PCV, Purge and EGR contribution?

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Paul Mechanic
Illinois
Paul
 

I have read everything you have done thus far. What are the fuel trims doing, but I assume this a speed density system? If you restrict some of the air entering the TB, do IAC counts start to increase?

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Kerry Mobile Technician
Ohio
Kerry
   

Along the lines of Paul's question, what happens when you return to idle after stabbing the throttle? Does the iac open under those conditions. I'm not a Honda expert but so far I haven't seen where the counts ever come off of zero…that would be helpful to know that the PCM is even capable of commanding it.? Might be worth making sure that the idler motor works fine by using a 9 volt battery…

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Interesting
Robert Technician
Michigan
Robert
 

I agree with Benjamin black ground wire . What does scanner show any PWM duty cycle should be ground side controlled ..Coolant flow blockage ? IAC wont shut and cant be diagnosed ..Sounds like a bad used valve unless you stuck a new $300 one on it .

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Andy Owner/Technician
Oregon
Andy
 

Is it a manual trans car if so check the neutral switch and the clutch pedal switch High ac voltage coming out if the alternator? Have Seen a number of idle fault codes from these on a variety of Asian makes and the clutch switch on a 98 civic Shorted wiring harness under the intake support bracket any number of wires can be making contact it’s hard to see and often hard to duplicate shine…

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Jason Owner/Technician
California
Jason
 

Thanks for all the suggestions. I have added an additional ground wire to g101, I have replaced the PCV valve with a Honda valve, I will look at fuel trims today, the computer will command the iac to over 0 when the a/c is turned on or the headlamps are used. The iac was replaced with the oem new one. If you plug off the iac port the idle drops down to around 400 RPM, or just above a stall. I…

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James Technician
California
James
 

Neutral safety switch, or clutch switch. If it thinks it is in neutral when you are in decell, it will set your code.

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